Apparatus for producing electrified powders by friction



March 25, 1952 HAMPEV 2,590,534

APPARATUS FOR PRODUCING ELECTRIFIED POWDERS BY FRICTION Original FiledJuly 23, 1947 INVENTOR. P/[RRIHAMPE ATTORNEY Patented Mar. 25, 1952APPARATUS Fort: PRODUCING IiLECTRIFIED POWDERS BY FRICTIONPierre'Hainpe,gYersaille's, France,'assignor of one half tosociete'dite'z Etablissemeiits & Laboratoires Georges-Truffaut,Versailles, France, a French company, and

Truffaut, Versailles, Sei

one-half to. Georges ne-et-oise, France originaiqapiuifiticn my 23,1947, Serial Ne.

763,132. Divided" and this 1949, Serial No. 21,1946

application July 22,

106,176. In France October infants. (01. ris -265') This inventionrelates to apparatus for imparting an electrical charge to particles of.a pulveru lent material and is more particularly} concerned withapparatus of the character indicated 'adapted for providing electrifiedparticles for agricultural and industrial powder spraying, forexample-the spray dusting of plants. I A w v In my copendingapplication, Serial No. 763,133, now abandoned, I have described aprocess for spraying electrified'powder particles and have dis closedthe possibility of electrifying powder particles by friction. I havefound thatin order to electrify the powder particles to a high degreeofeffectiveness, it is necessary to cause, all of the particles to comeinto contact with the friction surface and preferably to make severalsuccessive contacts. The provision of simple partitions arranged asbaflies is not sufficient to obtain the desired result since thecurrentof gas "carrying the particles to be electrified is defiected' b'y thebaffles which impart a rotary motion tothe current and this motion isalso imparted to thepa'rticles so that effective frictional contact isnot obtained. v

In accordance with the present invention, I provide means for insuringmultiple frictional contact between the particles and thefri'ctional surface, the means which I provide'comprisingtwo flat surfaces disposed inface to facerelationship and. between which the current of gas carryingthe powder particles is caused to pass. The flat surfaces may bevibrated.

I have also found that at the instant a powder particle comes intocontact with the friction surface, the particles must not be subjectedtoan opposed magnetic field, which may be caused either by the charge onadjacent powder particles or by the charge on the friction surface; Inaccordance with the invention, the friction members are arranged in suchmanner that the charges which are deposited thereon 'are symmetricalwith respect to the charges on the powder particles:

Furthermore, the electrified powder particle's must not be'allowed toadhere to the friction surface by electrostatic attraction, since thiswould prevent fresh particles from coming in contact with the surfaceand might cause blocking of the apparatus. In addition, electrifiedarticles must never be permitted to agglomerate', since" this would tendto permit the charges to escape. The apparatus of the invention preventsadherence and agglomeration of-the particles sincethe friction surfacesare so arranged'that-the' current of gas readily sweepsthe particlesalong.- V

The nature of the particles and ofthefriction 2 surfaces determines thepolarity of the charges, and to a certain extent the magnitude of thecharges. It has been determined which type of friction substance, hereinreferred to as triboelectric material, is most suitable for each type ofpowder. In the apparatus of the invention the opposed friction surfacesshould be formed from a" resilient friction substance which resistswear, since rapid wearing away of the material of the friction surfaceinterferes with the separation of the charges of opposite polarity. Careshould also be taken to avoid dampness since dampness adversely affectsfrictional electrification. Among the'substances which are particularlysuitable for constructing the opposed friction surfaces are rubber,horse-hair, threads, and sheets of plastic material.

When a powder is to be used which is difficult to electrify, the powdermay advantageously be mixed with another powder that holds an electriccharge well, such as sulphur, casein, anthraquinone and lime. Thepowders are generally mixed before they are passed between the frictionsurfaces but in some cases it is desirable to mix the powders only afterone of them has passed through the electrifying device, in order tofacilitate operation. I

, The powder particles which have been electrifled by being passedthrough my device as hereinabove described may, without furthertreatment, be directed on to the surface to be powdered. I alsocontemplate setting up an electrical field around the surfaces to bepowdered in order to accelerate precipitation. As mentioned, I provideapparatus for electrifying particles in accordance with the principlesset forth above comprising two leaves having opposed friction surfaceswhich are resilient or are resiliently held in contact. A current of gascarrying the powder to be electrified is blown between the leaves, theresiliency of the leaves permitting the air pressure to separate themand thus permit the gas-suspended powder particles to pass therebetween.The device provides a large area of contact and the friction surfaces ofthe leaves are close in contact so that the space between the surfacesis small. In my device a particle of powder passing between the twoleaves carrying equal charges of the same polarity is not subjected tothe electric field produced by such charges.

The speed of the air current between the leaves, the vibrations causedby said air current, and the choice of the substances used (rubber forexample) prevent the powder from heaping up between the leaves.

Since the leaves are very close together, particles of powder mightbecome locked between them, which would clog the apparatus. Thisdifficulty can be avoided by arranging the leaves in such a manner thatthe pressure of the air produced by the blower is capable, in case ofobstruction, of separating the adjacent leaves and of thereby uncloggingthe apparatus. Owing to this arrangement, it is even sometimesunnecessary to provide a permanent spacing between the two leaves; theair pressure moves them apart just enough to allow the powder to pass.It is moreover possible to make the leaves more or less readilyseparable, and even to make such separation adjustable, either by usingflexible leaves, or by holding them in contact with one another bypressure of a spring.

The nature of the surfaces of the leaves plays an essential part in theelectrification, since it is these surfaces which come into contact withthe powder. Said surfaces may be smooth, or provided with variousasperities, or provided with a covering of suitable composition.

Each leaf may be composed of two constituents or laminae, viz. aninternal constituent or lamina, chosen to provide maximumelectrification, and an external constituent or lamina, the function ofwhich is both to provide the requisite resilience and, by means of itsconductivity, to permit the electric charges developed on the frictionsurfaces to fiow away.

Finally, particular devices may be added for carrying away the charges,such as: metal blades, spikes, wires, etc. interposed between theleaves, imbedded in the leaves, or disposed on the outer surface of theleaves. Said devices may be effective either by decreasing the distancewhich the charges have to travel in a poor conducting substance, or bycausing the friction surfaces to discharge, by ionizing the adjacentgaseous medium.

The aforesaid leaves may be provided with numerous asperities or holes,whereby a construction is provided which is similar to a structurecharacterised by the presenceof numerous small obstacles.

The leaves may also be provided with longitudinal striae i. e. striaedisposed in the direction of flow of the particle carrying gas, which inefiect provides a plurality of parallel capillary tubes. i

A single stria may, however, be used.

In order to make the invention more clearly understood severalembodiments have been illustrated in the accompinying diagrammaticdrawings which are given by way of non-limitative examples.

Fig. 1 is a general longitudinal sectional view of an apparatus forproducing electrified powder. Fig. 2 is a similar section of amodification. Fig. 3 is a plan view corresponding to Fig. 2.

Fig. 4 shows a section of another modification.

Fig. 5 is a section through the line Il--H of Fig. 4.

Referring to Fig. 1, it will be seenthat the apparatus comprises a pumpP, by means of which air can be supplied to a receptacle A containingthe powder. Said pump is provided with a tube T opening between twowalls or leaves F1 and F2 which are pressed against one another by lightsprings 1'. The mixture of air and powder blown between the leaves movesthem apart and is electrified as it comes into contact with them. Acloud of electrified powder is obtained at N.

Figs. 2 and 3 show an electrifying device comprising two rubber leavesF1 and F2 which are fixed to a base S by means of laterally arrangedclamping strips L. The resilience of the rubber is suficient to enablethe air charged with powder blown through the tube T to pass through theapparatus in lengthwise direction. This device is suitable in particularfor electrifying powders mainly comprising lime, silica, metallicoxides, etc.

The device of Figs. 4 and 5 is similar to the previous one, but therubber leaves are replaced by thin flexible sheets C1, C2, on which asilk fabric has been cemented at D1, D2. The whole arrangement is heldfor example by means of rivets located on the sides. The powder passingbetween the two sheets is in direct contact with the silk. This deviceis suitable in particular for electrifying crushed sulphur.

Suitable provision is made in each instance to permit the electriccharges developed on the friction surfaces to flow away.

The springs r in Fig. 1, the clamping strips L in Figs. 2 and 3 and therivets in Figs. land 5 serve the further function of carrying away theaccumulated charge from the leaves.

The foregoing examples are not intended for any other purpose than toillustrate the principle of the apparatus. In particular, the nature ofthe leaves and the composition of the powders are essentially variable.The same applies'to the dimensions, the output, the shape and the numberof the leaves. It is understood, in particular, that the leaves may berectangular, triangular, circular, segment-shaped, etc. They may beflat, wound in the shape of concentric cylinders or of spiral, or foldedon themselves.

This application is a division of my copending application, Serial No.763,132 filed July 23, 1947.

I claim:

1. Apparatus for dusting plants and the like with electrically chargedparticles which comprises, in combination, means for supplying a streamof gas carrying particles to be charged, a passageway having closelyspaced parallel walls, means for directing the stream of gas betweensaid walls,,said walls normally being substantially in engagement withone another and being sufficiently yieldable to be separable by saidstream to permit free passage of said stream without clogging, theopposed faces of said walls being provided with a longitudinal striaeand means for conducting a charge away from said walls.

2. Apparatus for dusting plants and the like with electrically chargedparticles which comprises, in combination, means ,for supplying'a streamof gas carrying particles to be charged, closely spaced parallel leaves,means for directing the stream of gas between said leaves, said leavesnormally being substantially in engagement with one another and beingsufficiently yieldable to be separable by said stream to permit freepassage of said stream without clogging, the opposed faces of saidleaves being provided with apertures and means for conducting a chargeaway from said leaves.

' '3. Apparatus for dusting plants and the like with electricallycharged particles which comprises, in combination, means for supplying astream of gas carrying particles to be charged, a channel having closelyspaced parallel walls, means for directing the stream of gas betweensaid walls, said walls normally being substantially in engagement withone another and being sufficiently yieldable tobe separable by saidstream to permit free passage of said stream without clogging, the saidwalls being of a two-ply con.- struction comprising an innernon-conductive lamina and an outer conductive lamina and means forconducting a charge away from said walls.

4. Apparatus for dusting plants and thelike with electrically chargedparticles which comprises, in combination, means for supplying a streamof gascarrying particles to be charged, closely spaced parallel leaves,means for directing the stream of gas between said leavesabasesupporting, said leaves, means for securingthe longitudinal edges ofsaid leaves to said base said leaves normally being substantially. inengagement with one another and being sufliciently yieldable to beseparable by said stream to permit free passage of said stream withoutclogging, and means for conducting a charge away from said leaves.

5. Apparatus for dusting plants and the like with electrically chargedparticles, comprising means for supplying a stream of gas carryingparticles to be charged, means for charging said particles solely byfriction comprising a passageway having closely spaced yieldable wallsof triboelectric material providing opposed charging surfaces, means fordirecting the stream of gas carrying said particles between saidsurfaces whereby said particles are charged by repeated contact withsaid surfaces, said walls normally being substantially in engagementwith one another but being suificiently yieldable to be separated bysaid stream, means for thereafter directing the stream of gas carryingsaid charged particles toward the object to be dusted and means forconducting a charge away from said charging surfaces.

6. Apparatus for dusting plants and the like with electrically chargedparticles, comprising a tubular passageway having resilient walls, meansfor pressing opposite walls of said passageway yieldalbly together,means for forcing a stream of gas carrying particles to be chargedthrough said passageway, said Walls normally being substantially inengagement with one another but being sufficiently yieldable to beseparated by said stream, whereby said opposite walls are forced apartenough to permit passage of said stream and said particles are chargedby repeated contact with said walls, means for directing the stream ofgas issuing from said passageway toward the object to be dusted withsaid charged particles and means for conducting a charge away from saidcharging surfaces.

'7. Apparatus for dusting plants and the like with electrically chargedparticles, comprising a tubular passageway having opposed closelyadjacent resilient walls, means for forcing a stream of gas carryingparticles to be charged through said passageway whereby said oppositeresilient walls are forced apart sufficiently to permit passage of saidstream and said particles are electrically charged by repeated contactwith said walls, means for directing the stream of gas issuing from saidpassageway toward the object to be dusted with said particles and meansfor conducting a charge away from said charging surfaces.

8. Apparatus for dusting plants and the like with electrically chargedparticles, comprising a tubular passageway having opposed flexible sidewalls, means for resiliently pressing said opposed walls together atspaced intervals, means for forcing a stream of gas carrying particlesto be charged through said passageway whereby said opposed walls areforced apart only sufiiciently to permit passage of' said stream andsaid p'articles are electrically charged by repeated fric-' tionalcontact with said walls, means for directing the stream of gas issuingfrom said passageway toward the object to be dusted and means forconducting a charge away from said charging surfaces.

9. Apparatus for dusting plants and the like with electrically chargedparticles, comprising means for supplying a stream of gas carryingparticles to be charged, means for charging said particles solely byfriction comprising a passageway connected with said supplying means andcomprising closely spaced charging surfaces having a large surface areain relation to the crosssectional area of said passageway, said surfacesnormally being substantially in contact with one another but beingseparable by the force of said stream to prevent clogging of thepassageway while maintaining said surfaces close together so that saidparticles are charged by repeated frictional engagement with said wallsas the particles are carried through said passageway by the gas stream,means for directing the gas stream carrying the charged particles fromthe outlet of said passageway toward an object to be dusted and meansfor conducting a charge away from said charging surfaces.

10. Apparatus for dusting plants and the like with electrically chargedparticles which comprises, in combination, means for supplying a streamof gas carrying particles to be charged, a passageway having closelyspaced parallel Walls, means for directing the stream of gas andparticles between said walls, said walls being normally in engagementbut being sufficiently yieldable to be separated by said stream of gasand particles to permit substantially laminar flow of said gas throughthe passageway and provide repeated frictional engagement between saidwalls and particles to impart an electrostatic charge to said particlesand means for conducting a charge away from said walls.

11. Apparatus for dusting plants and the like with electrically chargedparticles, which comprises means for supplying a stream of gas carryingparticles to be charged, superposed parallel leaves of flexiblematerial, means for directing the stream of gas and particles betweenthe leaves, resilient means yieldably pressing said leaves substantiallyinto engagement with one another, said leaves being separated by saidstream of gas and particles to permit laminar flow of said gas betweenthe leaves and repeated frictional engagement between said particles andthe leaves to impart an electrostatic charge to said particles and meansfor conducting away from said leaves an opposite charge imparted to theleaves by said frictional engagement.

12. Apparatus for dusting plants and other objects with electricallycharged particles, comprising a tubular passageway having yieldablewalls,,means for pressing opposite walls of the passageway yieldablytogether, means for forcing a stream of gas through said passageway,means for introducing the particles to be charged into said stream inadvance of said passageway, the opposite walls of said passageway beingseparated by said stream to permit substantially laminar flow of gasbetween said walls with repeated fric tional engagement between saidparticles carried by the gas and said walls to impart an electrostaticcharge to said particles and an opposite 7 8 charge to said walls andmeans for removing said Number Name Date opposite charge from saidwalls.- 2,165,946 Smith July 11, 1939 PIERRE HAMPE- 2,302,185 Campbell,Jr. Nov. 17, 1942 2,302,289 Bramston-Cook Nov. 17, 1942 REFERENCES CITED5 2,396,533 Root Mar. 12, 1946 The following'references are of record inthe ,9 ad fi 1949 file of this patent:

OTHER REFERENCES UNITED STATES PATENTS A High Voltage D. c. Generator,by R. E. V011- Number Name Date rath, pages 298-304, Physical Review,v01. 42, No.

532,642 Crowell Jan. 15, 1895 2;"second series. Oct. 15, 1932.

628,670 McNamara, July 11, 1899 Static Electricity, U. S. Dept. ofCommerce, 1,405,613 Milliken Feb. 7, 1922 Nat. Bur. of Standards,Circular C438, (esp. pp. 2,114,682 Gumaer Apr. 19, 1938 9 and 34).

